This invention offers a simple reliable valve for, among other applications, reduction of pressure pulses in the supporting gas cushions of air cushion vehicles. It utilizes a low cost rugged design that is normally rotary in concept and that will operate for extended periods with little or not maintenance.
My Air Ride Boat Hull designs, as described in U.S. Pat. Nos. 4,392,445 and 4,739,719 among others, brought out the need for the instant invention. The Air Ride Boat Hull designs utilize a blower pressurized air cushion positioned in the underside of the hull where such pressurized air cushion supports approximately 85 percent of the weight of the boat. It is not uncommon, during normal operation in low sea states, to have an approximately two to six cycle per second (cps) pressure pulse or spike occur in the gas cushion since the cushion is in reality a large gas spring. These pressure pulses result in heave forces that act on the hull that are of significant magnitude to cause an uncomfortable ride.
As an example, the 368 passenger 109 by 34 foot "Metro Manhattan" Air Ride Surface Effect Ship (SES) Ferry built by Avondale Industries, New Orleans, that will go into operation in New York, experiences an approximate three cps pressure spiking when operating in one to two foot seas. The pressure spikes or pulses experienced can amount to approximately 40,000 pounds of force on the 340,000 pound hull during each pressure spike. This makes for an uncomfortable bouncy or what has been described as a "cobblestone" like ride for passengers. This "cobblestone" ride is characteristic of virtually all large air cushion craft, of which the Air Ride SES is a variant, when operating in small to moderate waves.
The U.S. Navy has funded work to resolve this ride problem in their SES's. The resulting solution is in the form of a Ride Control System (RCS) that is commercially manufactured in the United States. A similar system is now also manufactured in Sweden. These systems are very similar in that they sense air cushion pressures and other hull operating characteristics and feed such information into a microprocessor controller. The controller processes the input data and then outputs operating conditions to gas cushion vent valves and/or blower inlet flow control valves.
The gas cushion vent valves are operated in such manner so as to open and thereby vent pressure peaks as they occur in the air cushion. The blower inlet flow control valves accomplish essentually the same thing; however, they do so by restricting blower flow and pressure outputs in time with the pressure peaks. These on-the-market RCS's utilize valves that are made up of a series of Venetian blind type louvers that are set in a rectangular frame. The louvers can be closed to essentually shut off gas flow or operated at various degree of openess at frequencies that coincide with the pressure pulsing frequency in the air cushion.
Powered hydraulic actuators are used to operate the louvers at their required operating frequencies in both systems. Due to their inherent design characteristics, these 2 to 6 cps cycling hydraulically powered louver valves are expensive initially, largely due to the hydraulic systems, and require significant maintenance due to the two to six cps stop and start wear on joints, louvers, and hydraulic systems.
A main feature of the present invention overcomes the shortcomings of the just discussed start and stop cycling louver valves. The instant invention centers around an inherently simple and reliable cycling valve design that can be driven by low cost motors. This valve is intended to be applied mainly to control of air cushion vehicle cushion pressure pulses; however, it can be utilized wherever a need exists for a low cost reliable valve that is capable of rapid and continual cycling. The features and improvements offered by the instant invention are discussed in the following sections.